Due to the rapid growth in personal mobile communication devices, the wireless market is always looking for new ways to further miniaturize radio frequency (RF) front ends while reducing cost and power consumption. For many years, wireless transceivers and subsystems have relied upon high quality factor (Q) passives to implement oscillators, filters, and other key RF front-end circuitry elements. However, these discrete, off-chip components occupy large chip areas and require power-demanding interfacing circuits. As a result, a great deal of research effort has been devoted to the development of micromechanical resonators that are more amenable to direct integration with integrated circuits (ICs).
In the past few years, vibrating RF micro-electrical-mechanical-system (MEMS) resonator technology has emerged as a viable solution, most notably, the film bulk acoustic resonator (FBAR) and surface acoustic wave (SAW) resonator, which have already been successfully implemented into commercial products. Such micromechanical resonators can perform as well as, if not better than, their bulky conventional counterparts and facilitate the miniaturization and power reduction of conventional RF systems. However, these devices typically cannot be used when multi-frequency functionality on a single chip is needed.
Contour-mode MEMS resonators have been developed to address this issue. Unlike FBARs and SAW resonators, contour-mode resonators use lateral dimensions to define their resonating frequencies, thus enabling single-chip, multi-frequency functionality. However, there is still room for improvement with respect to lowering the motional resistance of these devices to enable matching to 50Ω electronics, while retaining low power consumption, small size, and simple manufacturing processes.